Extracellular nucleotides are universal and phylogenetically-ancient signalling molecules acting through specific membrane receptors: the seven ligand-gated P2X channels, and the eight G-protein-coupled P2Y receptors (the P2Y1,2,4,6,11,12,13,14 receptor subtypes)1,2. Endogenous ligands for P2Y receptors include adenine (ATP, ADP), uracil nucleotides (UTP, UDP) and, as more recently recognized, sugar nucleotides (e.g., UDP-glucose and UDP-galactose). Conversely, cysteinyl-leukotrienes (cysLTs) are peptide-conjugated lipid mediators generated by 5-lipoxygenase metabolism of arachidonic acid with established roles in bronchial asthma, acting through the CysLT1 and CysLT2 receptors3. Both P2Y receptors and CysLT receptors belong to the ∂ group of the GPCR rhodopsin family (the purin receptor cluster), which also includes the thrombin receptors and a large number of orphan GPCRs4. Among receptors in the purin cluster, GPR174 is one of the closest receptors to both P2Y and CysLT receptors, with a mean amino acid sequence identity of 31% with the eight recognized P2Y receptors and of 32 and 35% with CysLT1 and CysLT24.